Johnny Bull****s Good wrote:

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I prefer to design bridge output amps which eliminate the need for such
add on measures.



** Hogwash, it does no such thing.

Power up and down noises mostly originate in the pre-amp stages.

A speaker relay with a few seconds on-delay and fast off catches them PLUS any from the power stages too.



Also, it halves the supply rail voltage needed to drive
any particular load to a given power level which allows the use of lower
voltage rated output devices. It also improves immunity to strong RFI
field strengths and allows a simple fuse in the DC supply rail, whether
actual or, much better, an electronic circuit breaker (perhaps making use
of the speaker voltage to modulate the tripping point to make it detect
impedance overloads rather than relying on detection of a maximum current
limit alone which could still burn out the output devices at moderate
volume levels[1]) to provide protection without introducing unwanted
distortion when a fuse is used in series with the speaker load in
unipolar designs.


** A bridge mode output stage is *highly vulnerable to damage* if there is a short on the speaker line.

Normally, shorts on amplifier outputs go to ground *NOT* from one amp's output to another. The latter scenario is impossible to protect against with any form of VI limiting and amp makers offer no warranty against it.




..... Phil